1. Field of the Invention
The present invention relates to a display data processing circuit having a function to convert input display data to output display data according to coefficient setting value and a liquid crystal display device having the display data processing circuit.
The present application claims priority of Japanese Patent Application No.2001-192078 filed on Jun. 25, 2001, which is hereby incorporated by reference.
2. Description of the Related Art
As a display device for a TV (Television) set or a like, a CRT (Cathode Ray Tube) is conventionally widespread and display data having a gamma (γ) characteristic corresponding to a luminance characteristic of the CRT is transmitted from a broadcasting device side.
In contrast, since a liquid crystal panel being gradually and widely used in recent years has a luminance characteristic (or a transmittance) being different from the CRT, in order to correspond to display data having a gamma characteristic being suitable to the CRT, it is necessary to mount a display data processing circuit which can perform compensation (gamma correction) of a luminance characteristic between input display data and output display data.
In the display data processing circuit, by putting data showing a relation between input display data and output display data in a look-up table and by reading a content of the look-up table according to a value of the input display data, a measure is taken to prevent delays in tracing of the output display data from developing when the value of the input display data is changed.
FIG. 11 is a schematic block diagram showing an example of a configuration of a conventional display data processing circuit. As shown in FIG. 11, the conventional display data chiefly includes a processing section 101, a storing section 102, and a look-up table 103. The processing section 101 has an MPU (Micro Processor Unit) (not shown). The MPU operates, in accordance with a program, to read display data corresponding to a coefficient setting value required for a gamma correction and then to set the read display data on a register in the look-up table 103. The storing section 102 is made up of, for example, flush memories and stores all output display data corresponding to all input display data. The look-up table 103 holds display data read by the processing section 101 and outputs a value corresponding to input display data X contained in the held display data as output display data Y.
Next, operations of the conventional display data processing circuit will be described by referring to FIGS. 11 and 12. In the look-up table 103 in the conventional display data processing circuit shown in FIG. 11, conversions are made between input display data X and output display data Y according to a following equation (1):
 Y=(X/A)^Z×B  Equation(1)
where “X” denotes a gray-scale value of input display data, “Y” denotes a gray-scale value of output display data, “Z” denotes a coefficient setting value (for example, “gamma value”) made up of positive numbers to one decimal place, “A” denotes a number of gray-scale levels of input display data, “B” denotes a number of gray-scale levels of output display data, and “^” denotes a power calculation.
The storing section 102 stores values obtained by the equation of “Y=(X/A)^Z×B” corresponding to all values that the input display data X and the coefficient setting value Z can take on, in a form of a table. FIG. 12 shows a content of a table stored in the storing section 102 which is made up of values obtained by rounding off a gray-scale value of output display data given by the equation (1), when the input display data X=0 to 255, the coefficient setting value Z=0 to 6.3, the number of gray-scale levels of the input display data A=256, and the number of gray-scale levels of the output display data B=256. The processing section 101 reads data obtained from calculation of the term “(X/A)^Z×B” corresponding to all values that the input display data X can take on, according to a value of the coefficient setting value Z, and outputs the read data to the look-up table 103. The look-up table 103 holds the input data obtained from calculation of the term “(X/A)^Z×B”, reads a value obtained from the calculation of the term “(X/A)^Z×B” corresponding to a value of the input display data X according to input of the input display data X, and outputs the read value as output display data Y.
In the display data processing circuit shown in FIG. 11, values obtained by calculation of the term “(X/A)^Z×B” required to produce a register value of the look-up table 103 are stored in the storing section 102 in a manner that values correspond to all values to be obtained from a relation between the input display data X and the coefficient setting value Z.
Therefore, the conventional technology has a problem in that, when a range of a gray-scale value of input display data X is wide or when a range of a value that the coefficient setting value Z can take on is wide, memory capacity of the storing section 102 becomes large and, as a result, a rise in costs is unavoidable. Moreover, there is another problem in that use of many devices causes an increase in power consumption.